What is natural? The scale and consequences of marine bio invasions in the North Atlantic Ocean

PhD ceremony: Ms. D. Haydar, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: What is natural? The scale and consequences of marine bio invasions in the North Atlantic Ocean

Promotor(s): prof. W.J. Wolff

Faculty: Mathematics and Natural Sciences

The scale and consequences of marine bioinvasions are larger than is generally assumed, and natural ecosystems do not exist along North Atlantic coasts, concludes Deniz Haydar in her thesis. We have potentially overlooked hundreds of marine bioinvasions, which are not only inconspicuous species, but may also be key species in coastal communities.

Exotic, non-indigenous or invasive species are those species that are intentionally or unintentionally moved by humans outside their natural range. In the North Sea, the number of exotic species has dramatically increased in the past 30 years, which is consistent with world-wide patterns. One of the most important transport mechanisms for exotic species in the North Sea is the translocation of oysters for culturing purposes. These live oysters carry a rich epiflora and –fauna on their shells. Introducing a small number of oysters can result in a large number of associated introductions. This is due to the fact that a single oyster can carry a large number of species and individuals. Furthermore, the (exotic) Pacific oyster reefs in Dutch coastal waters form a substrate for newly arriving exotic species.

Organisms are by default considered native, unless there is evidence that they are introduced. Cryptogenic species are those species that are neither demonstrably native, nor introduced, and include historically overlooked invasions. Trans-Atlantic shipping has been taking place long before the first comprehensive biological surveys were carried out. Based on disjunct distribution patterns that cannot be explained by natural dispersal mechanisms, Haydar estimated the number of cryptogenic species and thereby the number of historical introductions in the North Atlantic Ocean.